#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>

int mu(int y)
{
	int z = 1;
	for (int j = 1; j <= y; j++) {
		z *= (2 * j + 1);
	}
	return (z);
}

int zi(int x)
{
	int a = 1;
	for (int i = 1; i <= x; i++) {
		a *= i;
	}
	return (a);
}

int main()
{
	double sum = 0;
	int n;
	scanf("%d", &n);
	for (int u = 1; u <= n; u++) {
		int e = zi(u - 1);
		int r = mu(u - 1);
		sum += (double)e / r;
	}
	printf("%.10lf", sum);
	return 0;
}